In most oceanic locations around the world the water at depths greater than 130 meters is relatively fresh, dark, and cold in comparison with the surface water, which is warmer and has a greater salinity. Various ocean thermal energy conversion (OTEC) inventions have been devised in the past to exploit these temperature and salinity gradients between the surface and deep ocean to produce power, or to create an upwelling of nutrient-rich deep water to the ocean surface for mariculture. For example, one simple method involves placement of a long vertical cold water pipe into the ocean in such a manner that the bottom of the pipe is exposed to cold, relatively fresh water, while the top of the pipe is in warm, saline water. A continuous flow of water up the pipe results after the fountain is primed, due to an exchange of heat, but not salinity, with the ambient ocean. H. Stommel, A. B. Arons, and D. Blanchard, "An Oceanographical Curiosity; the Perpetual Salt Fountain," Deep Sea Research, Vol. 3 (1955), pp. 152-155. A similar system for surface water-deep water counterflow is disclosed by Johnson, "Salinity-Driven Oceanographic Upwelling," U.S. Pat. No. 4,597,360, issued July 1, 1986.
A basic OTEC system for generation of power is disclosed by Claude, et al, "Method and Apparatus for Obtaining Power from Sea Water," U.S. Pat. No. 2,006,985, issued July 2, 1935. OTEC systems of this type have considerable appeal in that approximately sixty percent of the world's largest cities and two-thirds of the world's population live within 80 kilometers of the sea. However, existing OTEC systems have either been inefficient or not cost-effective due to a number of problems, such as the length of the large cold water pipe required; the size of heat exchangers, turbines, and evaporators; biofouling, corrosion, and creation of salt water gases; and the difficulty of transmitting electricity under water.
In contrast, in the present invention, hydraulic compression of the entrained air is used to assist in exhausting water at the bottom of the apparatus, thus increasing the flow through the generator. The present apparatus does not require extreme temperature differences, and thus can be located close to shorelines near most major cities. This serves to minimize the length of electrical transmission lines. The present invention does not involve cold water pipes, evaporators, condensers, or steam turbines. The heat exchanger is an inexpensive cooling tube which serves to limit biofouling and corrosion.